This invention relates to the preparing of vector data forming a plot, such as a line traces, graphs, geographic maps, etc. into raster data and more particularly the preparation vector data in vector band format for conversion into raster scan format in a high speed and efficient manner.
The conversion of known line information having Cartesian coordinate values forming a plot into a raster scan format for display on an image device or printout on a serial line printer is known in the art. Example of such conversions are illustrated in U.S. Pat. Nos. 3,430,207; 3,449,721 and 3,895,357. In general, vector information representing the various lines comprising the entire plot is received in the form of beginning and ending coordinates which may further be broken down in vector segments. This information may be encoded to form binary for the various vectors which are subsequently stored and retrieved for processing to form a series raster scan lines with values set in each line representing a line increment of the total vector or vectors "traversing" each such scan line. For line vectors that traverse laterally relative to the original x-y Cartesian coordinates, x and y values are generated from coordinate information and an algorithm is employed to calculate the slope of the line vector to properly position the line increment in each scan line as processed. An example of slope approximation for line vectors is shown in U.S. Pat. No. 3,544,972.
In recent times, electrostatic printer/plotters and electrostatic plotters have become popular for hard copy print out of graphic or plot information with on line host computer systems using graphics utility software in conjunction with a users application program. Such plotters include an array of electrodes or nibs which extend across a recording medium with the medium being incremented in a direction transverse to the nib array. On the opposite side of the medium is a plurality of counterelectrodes in vis-a-vis position to the nib array. The nibs are counterelectrodes and may be electrically addressed in a manner to provide deposits of charge in form of latent charge dots on the surface of incremented recording medium. The toner development of these latent charge dots provides a visible image. For further understanding of these printer/plotters, reference may be made to U.S. Pat. No. 4,054,885.
Vector processing systems for this type of printer/plotter operate within a conventional Cartesian coordinate system wherein line vectors are defined in terms of nib (dot) coordinates based upon the resolution (dots/inch) of the particular plotter. The origin of the coordinate system is based upon the first nib on the first writable scan line of the plot to be created, with the +y axis extending across the width of the recording medium and the +x axis extending in a direction opposite to incremental paper movement.
There is generally three phases in processing vector information from a host system employing graphics utility software. There is the vector generation phase, the vector ordering (including orientation) phase and vector to raster phase. In the vector generation phase, the host system resolves the application units of measure into the integer nib coordinate system of the plotter. In the vector ordering phase, the vectors, accumulated for a single plot, are ordered to the direction of the recording medium and are "sorted" into bands forming link chains, together which constitute the entire plot. In the third phase, the band ordered vectors are then processed into raster scan lines of incremental vector information. The raster scan information is stored until an entire band has been converted, at which time the information is sent on to the plotter for printout.
In general, the vector to raster conversion requires the most amount of the processing time of the host system. Also, the host system is not capable of rasterizing vector data at a rate sufficient to drive the plotter at its maximum plotting speed.
What is, therefore, desirable is to employ the plotter more efficiently, i.e., at higher output per unit time while also reducing the rasterization time and save host computer time by offloading vector to raster processing.
Available is an offloading vector to raster processor manufactured by Varian Associates of Palo Alto, Calif. under the registered trademark, GRAPHWARE. Under the operation of this processor, multiple readings, writings and processing for each vector is necessary by the processor and complete handling of the vector ordering with the organized bands of vector information is done by the host system. What is more desirable for plotter efficiency is to raster process vector data even more quickly with final fine vector ordering being also accomplished by the offloading vector to raster processor.